1. FIELD OF THE INVENTION
The present invention relates to a digital audio signal interleave sequence method for recording and reproducing digital audio signals on and from a video tape simultaneously with video signals using rotary heads.
2. DESCRIPTION OF THE RELATED ART
Digital audio recording or so-called pulse code modulation (PCM) recording of audio signals in the form of digitalized signals has made remarkable progress nowadays. Typical examples are compact disks (hereinafter abbreviated as CD) and rotary head type digital audio tape recorders (hereinafter abbreviated as R-DAT), which are described, for example, in (1) Nakajima and Ogawa, "Reading Book on Compact Disk", Ohm Publishing Company, Nov. 25, 1982 and (2) "Digital Audio Taperecorder System (R-DAT) recommended design standard 2nd Draft-", DAT Conference, Apr. 16, 1986.
As a means for obtaining a high quality of sounds in a video taperecorder (hereinafter abbreviated as VTR), a frequency modulation (FM) method has been adopted heretofore to realize high fidelity VTRs now popularized in the world. To further improve the sound quality, it is reasonable to consider that the PCM recording or digital audio recording method will take the place of the FM recording method.
During recording and reproducing digital audio signals on and from a medium such as a magnetic tape, a drop-out in reproduced data, i.e., a missing data phenomenon due to defects on the medium or some other reasons may occur. To avoid the drop-out, error correction codes or so-called redundancy data are added to original digital audio data to be recorded. Since a drop-out due to burst errors is quite above the capacity of error correction codes alone, a data dispersion method called an interleave has been adopted wherein burst errors are converted into random errors.
Interleave methods for converting burst errors into random errors are mainly divided into two types: a helical type interleave which adopts simple delays as used in CDs, and a block completed type interleave as used in R-DATs.
Because of separation of digitalized sounds by rotary heads of a VTR during recording and reproducing, it is generally preferable to adopt the block completed type interleave method which allows synchronization with the revolution period of the rotary heads. Thus, VTRs for business use now adopt the block completed type interleave method wherein independent tracks are provided for video and sound signals, and the sound signals are subjected to time compression for recording and reproducing (e.g., refer to S. Tujii et. al.; "Digital Audio Recording in M-II Format VTR" SMPTE 20th Television Conference No. 24, pp. 187 to 200, February 1986). However, for custom use VTRs which must essentially satisfy upper compatibility with current types in adding new functions, it is difficult to provide a new track dedicated to digital sounds. Therefore, a multiple recording method which records both sound and video signals at a time as in the FM recording method must be used. In such a case, if the block completed type interleave method is used with the completed period being that of a video field or frame, the total process time required becomes at least two times the completed period or more because the interleaving becomes complete at both the recording and reproducing sides, which results in a considerable time delay between analog video signals and digital sound signals. Such time delay will increase as editing or dubbing is repeated. On the other hand, although the helical type interleave method is complicated in processing signals due to its non-completed nature, it can process signals within a time corresponding to a so-called "interleave depth". Thus, assuming the same error correction ability as the block completed type interleave, the helical type interleave method can advantageously process signals within half the time required by the former, or less. The helical type interleave method has been applied to CDs for example. Contrary to the application to discs, the helical type interleave method has been found not always satisfactory in signal processing and error correction ability if it is applied to rotary head type VTRs for recording digital sound signals.